I tried this:
--------
Welcome to DrScheme, version 372 [3m].
Language: Textual (MzScheme, includes R5RS) custom.
> (immutable? 5)
false
>--------
I was surprised because it returns #f and not #t.
It is the correct behaviour, according to the manual. But, since it is
impossible to mutate 5, it is not the result I expected.
Gustavo